1. Field of The Invention
This invention relates to an improved optical-element holder, to which an optical element can be easily attached, and from which the optical element can be easily detached, with maintaining the profile irregularity of the optical element small (thus, with keeping the figure tolerance thereof fine).
2. Description of The Related Art
Generally, the following are known as means for holding or retaining an optical element.
Referring first to FIG. 9, there is shown a first example of a conventional optical element holder. In this figure, reference numeral 1 designates the optical element holder. Further, in a through hole 1A bored through the optical element holder 1, an enlarged cylindrical hole 1B of a diameter larger than the diameter of the through hole 1A (hereunder referred to simply as a counterbored stage portion 1B) is formed at an end of the through hole 1A. An optical element 2 such as a resonator mirror and a lens or the like is fitted into the counterbored stage portion 1B and is then fixed thereto with a Delrin ring 3 ("Delrin" is a trade name of an acetal resin manufactured by DuPont) and a screw ring 4. A male thread is cut on the outside surface of the screw ring 4. Further, the screw ring 4 is threaded into the counterbored stage portion 1B, on the inside surface of which a female thread is cut. The Delrin ring 3 is made of a synthetic resin and is pressed by the screw ring 4 upon the entire peripheral part of the surface 2A of the optical element 2. Thereby, the optical element 2 is fixed to the optical element holder 1.
Referring next to FIG. 10, there is shown a second example of a conventional optical element holder. In this figure, reference numeral 5 denotes a holding portion in which a fitting stage portion 6 for supporting the optical element 2 fitted thereto is provided. Three tapped holes 7 are formed in the peripheral part of the fitting stage portion 6. A fixing bolt 9 supporting a fixing plate 8 is screwed into each of the tapped holes 7. The fixing plate 8 is shaped like a flat plate. Further, a hemispherical supporting projection 8A is provided at an end of the fixing plate 8 and supports the optical element 2 at a point thereof fixedly by being put into abutting engagement therewith. The front surface 2A and the back surface 2B of the optical element 2 are securely supported by the fixing plate 8 and the fitting stage portion 6, respectively. Thus, the optical element 2 is firmly placed between the fixing plate 8 and the fitting stage portion 6. Consequently, the optical element 2 is held on the holding portion 5, with certain profile irregularity (or figure tolerance) of the optical element being maintained.
Additionally, in the case of a third example (not shown) of a conventional optical element holder, an optical element 2 is glued with adhesives directly onto both of a counterbored stage portion 1B of an optical element holder 1 and a fitting stage portion 6 of a holding portion 5 thereof.
The aforementioned examples of the conventional optical element holder, however, have the following drawbacks, respectively.
In the case of the first example of the conventional optical element holder, the optical element 2 is secured to the optical element holder 1 by the screw ring 4 through the Delrin ring 3. It is, however, difficult to maintain the profile irregularity (or fine figure tolerance) of a surface of the screw ring 4, on which the Delrin ring 3 is put into abutting engagement therewith, small. This results in that the pressing force of the screw ring 4, with which the surface 2A of the optical element 2 is pressed, becomes uneven. Consequently, a strain occurs in the surface 2A of the optical element 2. Therefore, the first example of the conventional optical element holder has a drawback in that the profile irregularity (or figure tolerance) of the optical element 2 can not be maintained small.
Further, in the case of the second example of the conventional optical element holder, the supporting projection 8A of the fixing plate 8 is put into direct abutment engagement with the surface 2A of the optical element holder 2 to thereby support the holder 2. Thus the supporting protection sometimes has an adverse effect upon the surface 2A of the holder 2. Practically, if the optical element 2 is fastened to the holding portion 5 with the fixing bolts 9 too tightly, distortions occur in the surface 2A of the optical element 2 around a portion of each of the supporting projections 8A, which is in abutting engagement with the surface 2A, as illustrated in FIG. 11. Consequently, the second example of the conventional optical element holder also has a drawback in that the profile irregularity (or figure tolerance) of the optical element 2 can not be maintained small.
Moreover, in the third example of the conventional optical element holder, the optical element 2 is glued with adhesives onto the optical element holder 1. However, there occur expansion and shrinkage in a portion of the surface 2A of the optical element 2, to which the adhesive is applied. Consequently, the expansion and shrinkage result in deformation of the surface 2A of the optical element 2. Therefore, the third example of the conventional optical element holder also has a drawback in that the profile irregularity (or figure tolerance) of the optical element 2 can not be maintained small.
The present invention is accomplished to eliminate the drawbacks of the conventional optical element holder.
Accordingly, an object of the present invention is to provide an improved optical element holder, by which an optical element can be securely held with maintaining the profile irregularity (or figure tolerance) of the optical element small, and from which the optical element can be easily detached.